JP5962131B2 - Polyethylene terephthalate composition - Google Patents

Description

The present invention relates to a polyethylene terephthalate composition having excellent hydrolysis resistance.

Polyethylene terephthalate is excellent in mechanical properties, thermal properties, chemical resistance, electrical properties, and moldability, and is used in various applications.
However, since the mechanical properties of polyethylene terephthalate decrease due to hydrolysis, various studies have been made to suppress hydrolysis when used over a long period of time or when used in a damp state. In particular, a solar cell front sheet film requires a service life of 20 years or more and optical characteristics outdoors, and therefore requires high hydrolysis resistance, elongation retention, and optical characteristics.

For example, Patent Document 1 describes a polyethylene terephthalate composition with less OCP insoluble matter with improved heat and moisture resistance, and a detailed description of a production method using a direct weight method.
However, when manufacturing by the direct weight method, although it is a trace amount, white foreign matter is generated and causes fish eyes, it is difficult to apply to optical use.
Patent Document 2 describes a method for producing polyethylene terephthalate with little foreign matter, but what is disclosed is a technique that contains 30 or more foreign matters (fish eyes) per 8 square centimeters, and is used for optical applications. Is insufficient.

WO2011 / 52290 JP 2007-70462 A

  An object of the present invention is to provide a polyethylene terephthalate composition that is excellent in hydrolysis resistance, elongation retention, and optical characteristics, and is suitable for solar cell film applications, by eliminating these conventional drawbacks.

That is, an object of the present invention is to provide an alkali metal phosphate compound as an alkali metal element in an amount of 1.0 mol / ton to 3.0 mol / ton, a diethylene glycol content of 1.0% to 1.5% by weight, phosphorus The compound contains 1.5 mol / ton or more and 5.0 mol / ton or less of phosphorus as elemental phosphorus, white foreign matter of 50 μm or more containing phosphorus element is 1 ppm or less in volume fraction, and the intrinsic viscosity is 0.60 dl / g or more and 0.70 dl. This is achieved by a polyethylene terephthalate composition having a carboxylic acid end group increase (ΔCOOH) of 50 eq / ton or less when subjected to wet heat treatment (155 ° C., 100% RH atmosphere for 4 hours).

According to the present invention, it is possible to provide a polyethylene terephthalate composition having excellent long-term hydrolysis resistance and optical properties. Moreover, by using the composition of the present invention as a biaxially stretched film, it is necessary to use magnetic materials, use electrical materials such as capacitors, use such as packaging, optical use, especially long-term hydrolysis resistance and optical properties. It can provide for the film use for a solar cell front sheet.

The polyethylene terephthalate composition of the present invention comprises an alkali metal compound as an alkali metal element in an amount of 1.0 mol / ton to 3.0 mol / ton, a diethylene glycol content of 1.0 wt% to 1.5 wt%, a phosphorus element Of white foreign matter of 50 μm or more containing phosphorus element and alkali metal element is 1 ppm or less in volume fraction, and the intrinsic viscosity is 0.60 dl / g or more and 0.70 dl. This is a polyethylene terephthalate composition having a carboxylic acid end group increase (ΔCOOH) of 50 eq / ton or less when subjected to wet heat treatment (155 ° C., 4 hours under 100% RH atmosphere).

  The polyethylene terephthalate composition of the present invention is a polyethylene terephthalate produced from terephthalic acid and ethylene glycol. The polyethylene terephthalate composition requires 98 mol% or more of all dicarboxylic acid components to be terephthalic acid and 98 mol% or more of all glycol components to be ethylene glycol from the viewpoint of mechanical properties, hydrolysis resistance, and heat resistance. is there.

  From the viewpoint of hydrolysis resistance, the alkali metal phosphate compound contained in the polyethylene terephthalate composition of the present invention needs to be 1.0 mol / ton or more and 3.0 mol / ton or less as an alkali metal element, Furthermore, it is preferably from 1.0 mol / ton to 2.0 mol / ton from the viewpoint of hydrolysis resistance.

  Examples of the alkali metal element of the present invention include sodium, potassium, lithium, etc. Among them, sodium is preferable from the viewpoint of hydrolysis resistance and white foreign matter, and sodium dihydrogen phosphate is hydrolysis resistance. From the point of view, it is preferable.

  The phosphorus element contained in the polyethylene terephthalate composition of the present invention is required to be 1.5 mol / ton or more and 5.0 mol / ton or less from the viewpoint of hydrolysis resistance, and more preferably 2.0 mol / ton or more. It is preferable from the point of hydrolysis resistance that it is 4.0 mol / ton or less. As the compound containing phosphorus element, phosphoric acid, phosphoric acid ester, and the like can be used in addition to the alkali metal phosphate compound. From the viewpoint of hydrolysis resistance, phosphoric acid and an alkali metal phosphate compound are used in combination. It is preferable.

The diethylene glycol content of the present invention is required to be 1.0% by weight or more and 1.5% by weight or less from the viewpoint of hydrolysis resistance and heat resistance.
The white foreign matter in the polyethylene terephthalate composition contains a phosphorus element and an alkali metal element, and when it is made into a film, it becomes a foreign matter (fish eye), so its content is the volume fraction of the polyethylene terephthalate composition. It is necessary that the rate is 1 ppm or less, more preferably 0.5 ppm or less, and particularly preferably 0 ppm.

  In order to reduce the white foreign matter to a volume fraction of 1 ppm or less, it is necessary to add an alkali metal phosphate compound in an ethylene glycol solution of 2.0 mmol / liter or more and 30 mmol / liter or less, and from the viewpoint of hydrolysis resistance. It is preferably 10.0 mmol / liter or more and 30 mmol / liter or less. White foreign matter is considered to be white foreign matter due to condensation reaction when the alkali metal phosphate compound touches the high-temperature ethylene terephthalate low polymer, and it is diluted to suppress the white foreign matter of the alkali metal phosphate compound. Addition in solution is required.

The polyethylene terephthalate composition of the present invention requires an increase in carboxylic acid end group (ΔCOOH) of 50 eq / ton or less when treated under steam at 155 ° C. for 4 hours from the viewpoint of hydrolysis resistance, In particular, it is preferably 40 eq / ton or less.
In order to reduce ΔCOOH to 50 eq / ton or less, it is effective to reduce the carboxylic acid end groups of the polyethylene terephthalate composition as much as possible. However, the decomposition reaction rate can be increased by using a buffer such as phosphoric acid / alkali metal phosphate. Inhibition is important from the viewpoint of hydrolysis resistance.

  The polyethylene terephthalate composition of the present invention needs to have an intrinsic viscosity of 0.60 dl / g or more and less than 0.70 dl / g from the viewpoint of hydrolysis resistance and film moldability.

  The polyethylene terephthalate composition of the present invention preferably contains a cocatalyst from the viewpoint of hydrolysis resistance. The co-catalyst should be at least one of manganese compounds such as manganese acetate and manganese hydroxide, magnesium compounds such as magnesium acetate, magnesium carbonate and magnesium hydroxide, and calcium compounds such as calcium acetate and calcium hydroxide. From the viewpoints of heat resistance and hydrolysis resistance. When such a cocatalyst is added, the sum (M) of 0.5 times moles of alkali metal elements and 1.0 times moles of cocatalyst metal elements in the polyethylene terephthalate composition, and phosphorus element (P) The molar ratio (M / P) is preferably 1.00 or more and 1.20 or less from the viewpoint of hydrolysis resistance and heat resistance.

The polyethylene terephthalate composition of the present invention can be produced by performing an esterification reaction by supplying a slurry of terephthalic acid and ethylene glycol to an ethylene terephthalate low polymer, and then performing a polycondensation reaction.
As the esterification reaction, a conventional method is used in which a slurry of ethylene terephthalate in a molten state is stirred at 240 ° C. or higher and 260 ° C. or lower, and a slurry of terephthalic acid and ethylene glycol is gradually added to distill water. be able to. The alkali metal phosphate compound needs to be added at any stage from the start of the esterification reaction to the start of the polycondensation reaction. The addition method of the alkali metal phosphate compound is required to be added as an ethylene glycol solution of 2.0 mmol / liter or more and 30 mmol / liter or less from the viewpoint of reducing white foreign matter, and more preferably 4.0 mmol / liter or more and 30 mmol / liter. The following is preferable. Moreover, when adding the ethylene glycol solution of an alkali metal phosphate compound, it is preferable from the point of a white foreign material reduction to add in the place stirred at the peripheral speed of 3.0 m / s or more and 30 m / s or less.

  Furthermore, between the time when the esterification reaction is substantially completed and the start of the polycondensation reaction, ethylene glycol is 0.1 mol times or more and 0.5 mol times with respect to all dicarboxylic acid components contained in the polyethylene terephthalate composition. By adding below, unreacted carboxylic acid end groups are esterified with ethylene glycol, and the amount of carboxylic acid end groups in the polyethylene terephthalate composition is reduced, thereby improving hydrolysis resistance.

As polycondensation reaction conditions, it is preferable from the viewpoint of hydrolysis resistance that the polycondensation reaction is performed at a final temperature of 275 ° C. or higher and 290 ° C. or lower.
As the polycondensation reaction catalyst, known compounds can be used, for example, antimony trioxide, titanium alkoxide, titanium chelate compound, germanium dioxide and the like. Among them, polycondensation reactivity, heat resistance To antimony trioxide.

  The polyethylene terephthalate composition thus obtained can be improved in hydrolysis resistance by performing solid phase polymerization and further reducing carboxylic acid end groups.

Although the specific manufacturing method of the polyethylene terephthalate composition of this invention is described below, it is not limited to this.
After melting the ethylene terephthalate low polymer in the esterification kettle, a slurry of terephthalic acid and ethylene glycol (ethylene glycol / terephthalic acid molar ratio: 1.15) is added over 3.5 hours to distill water. The esterification reaction is carried out. After completion of the esterification reaction, the reaction mixture was transferred to a polymerization reactor, and manganese acetate tetrahydrate ethylene glycol solution (5% by weight) as a co-catalyst was added as manganese acetate tetrahydrate to 100 parts by weight of the polyethylene terephthalate composition. Add 0.07 parts by weight of antimony trioxide as a polycondensation catalyst to 0.03 parts by weight. Here, when 0.1 mol times or more and 0.5 mol times or less of ethylene glycol is added to terephthalic acid, the esterification of unreacted carboxylic acid end groups proceeds efficiently by the cocatalyst, and hydrolysis resistance is increased. Can be improved. The amount of the cocatalyst added is 0.5 mol of the molar amount of the manganese element as the metal component contained in the cocatalyst and 0.5 mol of the sodium element as the alkali metal component contained in the sodium dihydrogen phosphate dihydrate. By making the ratio (M / P) of the sum (M) and the molar amount (P) of the phosphorus element to be 1.00 or more and less than 1.20, hydrolysis resistance is improved.

  After stirring for 5 minutes, ethylene glycol solution of sodium dihydrogen phosphate dihydrate (30 mmol / liter) as sodium dihydrogen phosphate dihydrate is 0.026 parts by weight with respect to 100 parts by weight of the polyethylene terephthalate composition. (Equivalent to 1.7 mol / ton) and 0.019 part by weight of phosphoric acid (equivalent to 1.9 mol / t) are added to the stirring site at a peripheral speed of 15 m / s. At this time, in order to adjust the white foreign matter to a volume fraction of 1 ppm or less with respect to the polyethylene terephthalate composition, the ethylene glycol solution of sodium dihydrogen phosphate dihydrate is 2.0 mmol / liter to 30 mmol / liter. In particular, it is preferable to add to a place where stirring is performed at a peripheral speed of 3.0 m / s to 30 m / s. Furthermore, in order to make the increase amount of carboxylic acid end groups after wet heat treatment be 50 eq / ton or less, the content of sodium dihydrogen phosphate dihydrate with respect to the polyethylene terephthalate composition is 1.0 mol / ton or more and 3.0 mol. / Ton or less.

  The polycondensation reaction is carried out at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr. When the melt viscosity reaches an intrinsic viscosity of 0.65, the polyethylene terephthalate of the present invention is formed by chipping with a strand cutter. A composition can be obtained.

  The polyethylene terephthalate composition thus obtained can be dried, extruded with a normal extruder, a T-die and biaxially stretched, and has hydrolysis resistance required for a solar cell front sheet. , The optical characteristics are good.

(A. Intrinsic viscosity: IV)
0.1 g of the polymer was dissolved in 10 ml of o-chlorophenol at 160 ° C. for 20 minutes and measured at 25 ° C.

(B. Determination of phosphorus content and manganese content in polymer)
The measurement was performed using a fluorescent X-ray analyzer (model number: 3270) manufactured by Rigaku Corporation.

(C. Determination of alkali metal content in polymer)
Quantification was performed by atomic absorption analysis (manufactured by Hitachi, Ltd .: polarized Zeeman atomic absorption photometer 180-80, frame: acetylene-air).

(D. Carboxylic acid end group amount)
An unstretched sheet sample was taken and measured by the method of Malice. (Reference MJ Mauleice, F. Huizinga. Anal. Chim. Acta, 22 363 (1960)).

(E. Method for measuring diethylene glycol)
0.5 g of polymer chip was amine-decomposed in monoethanolamine, and the released diethylene glycol was measured by gas chromatography. The numerical value is the weight percent of diethylene glycol in the polymer.

(F. Determination of white foreign matter in polymer)
5 g of polymer strands or chips were weighed on a black mount, and white foreign matters were marked using ENV-B manufactured by Otsuka Optical Co., Ltd. The marked white foreign matter was observed by SEM, and the white foreign matter having a maximum diameter of 50 μm or more was subjected to elemental analysis by SEM-EDX.
The number of white foreign matters in which phosphorus element and alkali metal element were detected was counted, the sphere equivalent volume was calculated from the maximum diameter, and the volume fraction of the white foreign total volume with respect to the polyethylene terephthalate composition was calculated.
However, the specific gravity of the polyethylene terephthalate composition is 1.35 g / cm ³ .

(G. Hydrolysis resistance evaluation: ΔCOOH)
A chip of the polyethylene terephthalate composition was treated in steam at 155 ° C. for 4 hours.
Measuring device: PRESSER COOKER 306SIII (manufactured by HIRAYAMA Mfg. Co., Ltd.)
Carboxylic acid end group increase (ΔCOOH) was evaluated on samples before and after treatment.

(Measurement of H. fish eye)
Using a polarizing plate, fish eyes per A4 size of a biaxially stretched film (thickness 50 μm) of a polyethylene terephthalate composition were marked, and the presence or absence of a phosphorus element and an alkali metal element was confirmed by SEM-EDX. A film in which the number of fish eyes containing phosphorus element and alkali metal element was 0 / A4 was accepted.

Example 1
In an esterification reactor (ES can) in which 114 parts by weight of bishydroxyethylene terephthalate (equivalent to 100 parts by weight of PET) was previously charged, a slurry consisting of 86 parts by weight of terephthalic acid and 37 parts by weight of ethylene glycol was 3.5 hours by a snake pump. The esterification reaction was carried out while controlling the temperature of the reaction product at 245 ° C to 255 ° C.

  After completion of the esterification reaction, 114 parts by weight of the obtained bishydroxyethylene terephthalate (equivalent to 100 parts by weight of PET) was transferred to a polymerization can, and 0.07 part by weight of manganese acetate tetrahydrate (5% ethylene glycol solution, elemental manganese) As an equivalent to 2.8 mol / ton), and 0.03 part by weight of antimony trioxide was added. Thereafter, 0.019 parts by weight of phosphoric acid (equivalent to 1.9 mol / ton) and 0.027 parts by weight of sodium dihydrogen phosphate dihydrate (equivalent to 1.7 mol / ton) were added in a 25 mmol / L ethylene glycol solution. The mixture was added to a place where stirring was performed at a peripheral speed of 4 m / s, the pressure was reduced while raising the temperature from 255 ° C. to 285 ° C., and the polycondensation reaction was performed at a final temperature of 285 ° C. and a degree of vacuum of 0.1 Torr. The resulting polyethylene terephthalate composition has an intrinsic viscosity of 0.65 dl / g, 1.3% by weight of diethylene glycol, a phosphorus element content of 3.1 mol / ton, a sodium metal content of 1.7 mol / ton, a carboxylic acid end group of 25 eq / ton. , ΔCOOH is 39 eq / ton and white foreign matter content is 0 ppm (the obtained polymer chip 5 g is observed with a magnifying glass (ENV-B manufactured by Otsuka Optical Co., Ltd., no detection)) and within the scope of the present invention. there were. At this time, the reason why the phosphorus element content is decreased with respect to the added amount is that the phosphorus compound was scattered out of the system together with ethylene glycol during the polycondensation reaction.

The obtained polyethylene terephthalate was dried and crystallized at 160 ° C. for 6 hours, then supplied to an extruder under a nitrogen atmosphere, rapidly cooled from a T-die with a casting drum (20 ° C.) at an extrusion temperature of 280 ° C., and electrostatically applied. After the sheet is formed by the above method, the film is longitudinally stretched at a longitudinal stretching temperature of 90 ° C. and a longitudinal stretching ratio of 3.8 times, and then stretched at a transverse stretching temperature of 110 ° C. and a transverse stretching ratio of 3.8 times, and heat treatment is performed at 230 ° C. Second, a biaxially stretched film having an effective magnification and a surface magnification of 13.2 was obtained. The results are shown in Tables 1 and 2.
The resulting biaxially stretched film had 0 fish eyes due to white foreign matter / A4, and was at a level that would not cause any problems even when used for solar cell front sheet applications.

(Example 2)
Polyethylene terephthalate composition and biaxially stretched film in the same manner as in Example 1 except that 11 parts by weight of ethylene glycol (corresponding to 0.35 mol times with respect to the terephthal component) is added after the addition of manganese acetate tetrahydrate. Got. The results are shown in Tables 1 and 2.
As a result of adding ethylene glycol, the obtained polyethylene terephthalate composition has 21 eq / ton of carboxylic acid end group and 35 eq / ton of ΔCOOH, which has improved hydrolysis resistance compared to Example 1, and is biaxially stretched. Even if the film was used for a solar cell front sheet, etc., it was at a level where there was no problem.

(Examples 3-5, Comparative Examples 1-3, 7)
A polyethylene terephthalate composition and a biaxially stretched film were produced in the same manner as in Example 1 except that the type and amount of the alkali metal phosphate compound, the peripheral speed, the concentration of the alkali metal phosphate compound ethylene glycol solution, and the intrinsic viscosity were changed. Filmed. The results are shown in Tables 1 and 2.

  In Example 3, when potassium dihydrogen phosphate anhydride was used instead of sodium dihydrogen phosphate dihydrate, white foreign matter tended to increase to 0.3 ppm, but within the scope of the present invention. There was no problem even if it was used for solar cell front sheet use.

  In Example 4, when the peripheral speed was changed to 2 m / s, white foreign matter tends to increase to 0.3 ppm, but it is within the scope of the present invention, and there is a problem even if it is used for solar cell front sheet applications and the like. There was no level.

  In Example 5, when the concentration of the sodium dihydrogen phosphate dihydrate ethylene glycol solution was changed to 30 mmol / L, white foreign matter tends to increase to 0.7 ppm, but this is within the scope of the present invention. Even if it was used for a solar cell front sheet, etc., it was at a level where there was no problem.

  In Comparative Example 1, the intrinsic viscosity of the polyethylene terephthalate composition was changed to 0.58 dl / g. Since the intrinsic viscosity is below the lower limit of the range of the present invention, the melt viscosity is lowered due to insufficient polymerization during melt film formation, film breakage frequently occurs due to strength reduction, and an evaluable biaxially stretched film cannot be obtained. It was a polyethylene terephthalate composition having insufficient film-forming properties.

  In Comparative Example 2, the intrinsic viscosity of the polyethylene terephthalate composition was changed to 0.71 dl / g. Since the intrinsic viscosity exceeds the upper limit of the present invention, the polymerization time is increased, the amount of diethylene glycol is increased to 1.6% by weight, and the carboxylic acid end groups are increased to 30 eq / ton. As a result, ΔCOOH is 53 eq / ton. It was out of the range, and the hydrolysis resistance was insufficient.

  In Comparative Example 3, a polyethylene terephthalate composition was obtained in the same manner as in Example 1 except that the alkali metal phosphate compound was not added. The obtained polyethylene terephthalate composition had a ΔCOOH of 63 eq / ton outside the scope of the present invention, and was insufficient in hydrolysis resistance.

  In Comparative Example 7, when the concentration of the sodium dihydrogen phosphate dihydrate ethylene glycol solution was changed to 35 mmol / L, white foreign matter was 2.4 ppm, which was outside the scope of the present invention, and the biaxially stretched film fisheye 7 / A4 were detected, and the optical properties were insufficient.

(Example 6)
The concentration of sodium dihydrogen phosphate dihydrate ethylene glycol solution was adjusted to 5 mmol / L, and sodium dihydrogen phosphate dihydrate ethylene glycol solution was added as a mixed slurry with terephthalic acid during the esterification reaction. A polyethylene terephthalate composition and a biaxially stretched film were obtained in the same manner as in Example 2 except that the addition was performed while stirring at a peripheral speed of 25 m / s over 5 hours. The results are shown in Tables 1 and 2.
The obtained polyethylene terephthalate composition had a ΔCOOH of 37 eq / ton and a white foreign matter of 0 ppm, which was within the scope of the present invention, and was at a level that would not cause a problem even when used for a solar cell front sheet.

(Example 7)
Sodium dihydrogen phosphate dihydrate ethylene glycol solution is prepared at two concentrations of 2.5 mmol / L and 12.5 mmol / L. The 2.5 mmol / L solution was added as a mixed slurry with terephthalic acid over a period of 3.5 hours while stirring at a peripheral speed of 25 m / s, and the other 12.5 mmol / L solution was bishydroxyethylene. After transferring 114 parts by weight of terephthalate (equivalent to 100 parts by weight of PET) to the polymerization can, it was added in the same manner as in Example 2 to obtain an ethylene terephthalate composition. The results are shown in Tables 1 and 2.
The obtained ethylene terephthalate composition had a ΔCOOH of 36 eq / ton and a white foreign matter of 0 ppm, which was within the scope of the present invention, and was at a level that would not cause a problem even when used for a solar cell front sheet.

(Examples 8 to 16, Comparative Examples 4, 6, 8, and 9)
Polyethylene terephthalate composition and biaxiality in the same manner as in Example 2 except that the addition amount and addition method of the alkali metal phosphate compound, the addition amount of phosphoric acid, the addition amount of manganese acetate as a co-catalyst, and the intrinsic viscosity are changed. A stretched film was obtained. The results are shown in Tables 1 and 2.

In Example 8, as a result of changing the addition amount of phosphoric acid, the molar ratio of phosphoric acid / sodium dihydrogen phosphate dihydrate was reduced to 0.74, and M / P was increased to 1.43. Therefore, ΔCOOH is 42 eq / ton and the hydrolysis resistance tends to be lower than that in Example 2. However, it is within the scope of the present invention and is at a level that does not pose a problem even when used for solar cell front sheet applications. It was.
In Example 9, as a result of changing the addition amount of phosphoric acid, the molar ratio of phosphoric acid / sodium dihydrogen phosphate dihydrate was increased to 1.47, so that ΔCOOH was 41 eq / ton and Example 2 However, it is within the scope of the present invention and is at a level that does not pose a problem even when used for solar cell front sheet applications.

  In Example 10, as a result of changing the addition amount of sodium dihydrogen phosphate dihydrate and changing the addition amount of phosphoric acid, the molar ratio of phosphoric acid / sodium dihydrogen phosphate dihydrate was 1. .90 and M / P increased to 1.43, respectively, and ΔCOOH was 41 eq / ton and the hydrolysis resistance tended to be lower than that of Example 2, but within the scope of the present invention. Even if it was used for a solar cell front sheet, etc., it was at a level where there was no problem.

  In Example 11, as a result of changing the addition amount of sodium dihydrogen phosphate dihydrate, the addition amount of phosphoric acid was changed to 2.8 mol / ton close to the upper limit value of the present invention. Since the molar ratio of sodium dihydrogen acid dihydrate was reduced to 0.68, ΔCOOH was 39 eq / ton and the hydrolysis resistance tended to be lower than in Example 2, and sodium dihydrogen phosphate Since the amount of dihydrate added is close to the upper limit of the range of the present invention, white foreign matter tends to increase to 0.1 ppm. However, it is within the range of the present invention and is used for solar cell front sheet applications and the like. It was a level without any problem.

  In Example 12, by changing the addition amount of sodium dihydrogen phosphate dihydrate, phosphoric acid, and manganese acetate tetrahydrate, the amount of phosphorus element was 1.7 mol / ton, the lower limit of the range of the present invention. However, the hydrolysis resistance tends to be lower than that of Example 2 with ΔCOOH of 38 eq / ton. There was no level. Moreover, compared with Example 10, since the molar ratio of phosphoric acid / sodium dihydrogen phosphate and M / P are within the more preferable range of the present invention, the hydrolysis resistance is improved.

  In Example 13, as a result of adding 2.8 mol / ton of sodium dihydrogen phosphate dihydrate and 2.8 mol / ton of phosphoric acid, the content of phosphorus element was 4.8 mol / ton, which was the upper limit of the present invention. Since the M / P is as low as 0.88, ΔCOOH tends to increase to 48 eq / ton, and white foreign matter is also detected at 0.1 ppm. However, it is within the scope of the present invention and is used for a solar cell front sheet. It was at a level where there was no problem even if it was used.

  In Example 14, as a result of adding 2.5 mol / ton of sodium dihydrogen phosphate dihydrate, the ratio of phosphoric acid / alkali metal phosphate compound became 0.76, so ΔCOOH increased to 39 eq / ton. The white foreign matter was detected at 0.1 ppm, but it was within the scope of the present invention and was at a level that would not cause a problem even if it was used for a solar cell front sheet.

In Example 15, by changing the intrinsic viscosity to 0.6 dl / g, the polymerization reaction time is shortened, and the amount of diethylene glycol tends to decrease to 1.0 wt% and the amount of carboxylic acid end groups to 20 eq / ton. However, it was within the scope of the present invention and was at a level that would not cause a problem even if it was used for a solar cell front sheet.
In Example 16, by changing the intrinsic viscosity to 0.68 dl / g, the polymerization reaction becomes longer, and the amount of diethylene glycol tends to increase to 1.4 wt% and the amount of carboxylic acid end groups to 22 eq / ton. However, it was within the scope of the present invention and was at a level that would not cause a problem even if it was used for a solar cell front sheet.

  In Comparative Example 4, when the addition amount of phosphoric acid was changed as compared with Example 12, the amount of phosphorus element was 0.9 mol / ton, which is outside the scope of the present invention, and therefore ΔCOOH was 70 eq / ton and resistance to resistance. Hydrolyzability was insufficient.

In Comparative Example 6, when sodium dihydrogen phosphate dihydrate ethylene glycol solution was added at a concentration of 1.0 mmol / L, ΔCOOH was 55 eq / ton and hydrolysis resistance was insufficient. This is presumed that because the sodium dihydrogen phosphate dihydrate ethylene glycol solution was too thin, a large amount of ethylene glycol was brought into the reaction system, resulting in an increase in diethylene glycol and a decrease in hydrolysis resistance. (Equivalent to 0.5% by weight of diethylene glycol = 1 mol%)
In Comparative Example 8, since sodium dihydrogen phosphate exceeds 3.5 mol / ton, which is the upper limit of the present invention, the molar ratio of phosphoric acid / sodium dihydrogen phosphate dihydrate is reduced to 0.56. , ΔCOOH was 74 eq / ton and white foreign matter was 1.4 ppm, which was outside the scope of the present invention, and the fisheye of the biaxially stretched film was 5 / A4, which was insufficient in hydrolysis resistance and optical properties.

  In Comparative Example 9, the amount of phosphorus was 5.6 mol / ton, which exceeded the upper limit of the present invention, the molar ratio of phosphoric acid / sodium dihydrogen phosphate dihydrate increased to 2.94, and M / P was As a result of reduction to 0.64, ΔCOOH was 80 eq / ton and hydrolysis resistance was insufficient.

(Comparative Example 5)
The esterification reaction was carried out in the same manner as in Example 6 except that the concentration of sodium dihydrogen phosphate dihydrate ethylene glycol solution was 1 mmol / L. Sodium dihydrogen phosphate dihydrate ethylene glycol solution concentration However, since the amount of ethylene glycol was excessively 5.75 mol times as much as the terephthalic acid, the rectifying tower temperature could not be controlled and a polyethylene terephthalate composition could not be obtained. . The results are shown in Tables 1 and 2.

Claims (1)

  The alkali metal phosphate compound is contained in an amount of 1.0 mol / ton to 3.0 mol / ton as an alkali metal element, the diethylene glycol content is 1.0 wt% to 1.5 wt%, and the phosphorus element is 1.5 mol / ton. Ton or more and 5.0 mol / ton or less, white foreign substance of 50 μm or more containing phosphorus element and alkali metal element is 1 ppm or less in volume fraction, intrinsic viscosity is 0.60 dl / g or more and less than 0.70 dl / g, moisture A polyethylene terephthalate composition having an increased amount of carboxylic acid end groups (ΔCOOH) of 50 eq / ton or less when heat-treated (155 ° C., 4 hours in 100% RH atmosphere).